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971.
Novel thiosemicarbazonato complexes of gold(III) have been prepared from reactions of [Au(damp-C1,N)Cl2(damp- = 2-(N,N-dimethylaminomethyl)phenyl) or [NBu4][AuCl4] with 2-pyridineformamide thiosemicarbazones (HL). The thiosemicarbazones deprotonate and coordinate as mononegative, tridentate NNS ligands to gold to give [Au(Hdamp-C1)(L)]Cl2 or [AuCl(L)]Cl complexes. The organometallic damp- ligand is protonated during the reactions and the Au-N bond is cleaved. The [AuCl(L)]+ cations represent the first gold(III) complexes with thiourea derivatives which are not stabilised by an additional organometallic ligand. Reactions of [NBu4][AuX4](X = Cl, Br) with diphenylthiocarbazone (dithizone) result in reduction of the metal and the formation of gold(I) complexes of the composition [AuX(SCN4-3,4-Ph2)] where SCN4-3,4-Ph2 is 3,4-diphenyltetrazole thione which is formed from cyclisation of dithizone. 相似文献
972.
The ion-exchange properties of two P2-type layered NaxMnO2 bronzes (x=0.6, 0.75) with a differential microstructure were studied in LiCF3SO3 solutions in acetonitrile under ambient conditions. Na+ ions are readily exchanged with Li+, but the reaction causes a significant loss of crystallinity that results in some amorphization. The feasibility of the process increases with increasing structural disorder in the parent compound; conversion, however, is incomplete. The ability of the exchanged material to intercalate water in the air is consistent with the formation of an Li-Mn-O compound that retains the layered framework. Also, the electrochemical data obtained for this material as cathode in lithium cells are consistent with retention of the layer structure and exclude a potential spinel transition due to the ion-exchange reaction. However, the cycling properties of cells made from these layered compounds are quite modest, probably because of the strong structural disorder induced by the lithium reaction. 相似文献
973.
The reactions of 3-methoxyphenyl, 3-chlorophenyl, and 4-cyanophenyl 4-nitrophenyl thionocarbonates (1, 2, and 3, respectively) with a series of secondary alicyclic amines are studied kinetically in 44 wt % ethanol-water at 25.0 degrees C and an ionic strength of 0.2 M (KCl). Pseudo-first-order rate coefficients (k(obsd)) are obtained for all reactions (amine excess was used). The reactions of compound 1 with piperidine, piperazine, and 1-(2-hydroxyethyl)piperazine and of compounds 2 and 3 with these amines and morpholine exhibit linear k(obsd) versus amine concentration plots with slopes (k1) independent of pH. In contrast, the plots are nonlinear upward for the reactions of substrate 1 with morpholine, 1-formylpiperazine, and piperazinium ion and of substrates 2 and 3 with the two latter amines. For all these reactions, a reaction scheme is proposed with a zwitterionic tetrahedral intermediate (T+/-), which can be deprotonated by an amine to yield an anionic intermediate (T-). When the nonlinear plots are fit through an equation derived from the scheme, rate and equilibrium microcoefficients are obtained. The Br?nsted-type plots for k1 are linear with slopes of beta1 = 0.22, 0.20, and 0.24 for the aminolysis of 1, 2, and 3, respectively, indicating that the formation of T+/- (k1 step) is rate-determining. The k1 values for these reactions follow the sequence 3 > 2 > 1, which can be explained by the sequence of the electron-withdrawing effects from the substituents on the nonleaving group of the substrates. 相似文献
974.
Jana Sopkov‐de Oliveira Santos Pierre Verhaeghe Jean‐Franois Lohier Pascal Rathelot Patrice Vanelle Sylvain Rault 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):o643-o645
The crystal structures of closely related quinoline compounds substituted at the 2‐position by a vinyl group, either including a Cl atom [2‐(1‐chloro‐2‐methylprop‐1‐enyl)‐8‐nitroquinoline, C13H11ClN2O2, (I)] or not [2‐(2‐methylprop‐1‐enyl)‐8‐nitroquinoline, C13H12N2O2, (II)], show an important deviation of the vinyl group from coplanarity with the quinoline ring system if the Cl atom is present. The nitro group is perpendicular [in (II)] or nearly so [in (I)] to the quinoline ring system. In (II), all non‐H atoms except the nitro O atoms are located on a crystallographic mirror plane. 相似文献
975.
Camila S. Xavier R. A. Candeia M. I. B. Bernardi S. J. G. Lima E. Longo C. A. Paskocimas L. E. B. Soledade A. G. Souza Iêda M. G. Santos 《Journal of Thermal Analysis and Calorimetry》2007,87(3):709-713
Magnesium and zinc ferrites
have been prepared by the polymeric precursor method. The organic material
decomposition was studied by thermogravimetry (TG) and differential thermal
analysis (DTA). The variation of crystalline phases and particle morphology
with calcination temperature were investigated using X-ray diffraction (XRD)
and scanning electronic microscopy (SEM), respectively. The colors of the
ferrites were evaluated using colorimetry. Magnesium ferrite crystallizes
above 800°C, presenting a yellow- orange color with a reflectance peak
at the 600–650 nm range, while zinc ferrite crystallizes at 600°C,
with a reflectance peak between 650–700 nm, corresponding to the red-brick
color. 相似文献
976.
Mauro L. Franco Dalva E. C. Ferreira Hélio F. Dos Santos Wagner B. De Almeida 《International journal of quantum chemistry》2007,107(3):545-555
Quantum chemical methods were used for the theoretical determination of the conformational population for the relevant conformers of cyclononane, i.e., TBC, TCB, TCC, and M4 (or C1), which have been previously investigated experimentally through detailed examination of the nuclear magnetic resonance (NMR) spectrum. Our best Gibbs free energy result, evaluated with MP4(SDTQ)/6‐31G(d,p)//MP2/6‐31G(d,p) energy differences and MP2/6‐31G(d,p) thermal corrections, lead to a temperature‐dependent population in excellent agreement with the experimental results based on the analysis of the low temperature 13C NMR spectrum. The nice agreement with experiment is achieved using MP2 harmonic frequencies for the evaluation of vibration partition functions within the standard statistic thermodynamics formalism. Theoretical temperature‐dependent infrared (IR) and 13C NMR spectra were simulated and compared with experimental data, which confirmed the ab initio conformational population reported here. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
977.
Perspectives on bioenergy and biotechnology in Brazil 总被引:4,自引:0,他引:4
Adalberto Pessoa-Jr Inêes Conceição Roberto Marcelo Menossi Raphael Revert dos Santos Sylvio Ortega Filho Thereza Christina Vessoni Penna 《Applied biochemistry and biotechnology》2005,121(1-3):59-70
Brazil is one of the world’s largest producers of alcohol from biomass at low cost and is responsible for more than 1 million
direct jobs. In 1973, the Brazilian Program of Alcohol (Proalcool) stimulated the creation of a bioethanol industry that has
led to large economic, social, and scientific improvements. In the year 1984, 94.5% of Brazil’s cars used bioethanol as fuel.
In 2003/2004, 350.3 million of sugarcane produced 24.2 million t of sugar and 14.4 billion L of ethanol for an average 4.3
million cars using ethanol. Since its inception, cumulative investment in Proalcool totals US$11 billion, and Brazil has saved
US$27 billion in oil imports. The ethanol production industry from sugarcane generates 152 times more jobs than would have
been the case if the same amount of fuel was produced from petroleum, and the use of ethanol as a fuel is advantageous for
environmental reasons. In 2003, one of the biggest Brazilian ethanol industries started consuming 50% of the residual sugarcane
bagasse to produce electrical energy (60 MW), a new alternative use of bioenergy for the Brazilian market. Other technologies
for commercial uses of bagasse are in development, such as in the production of natural fibers, sweeteners (glucose and xylitol),
single-cell proteins, lactic acid, microbial enzymes, and many other products based on fermentations (submerged and semisolid).
Furthermore, studies aimed at the increase in the biosynthesis of sucrose and, consequently, ethanol productivity are being
conducted to understand the genetics of sugarcane. Although, at present, there remain technical obstacles to the economic
use of some ethanol industry residues, several research projects have been carried out and useful data generated. Efficient
utilization of ethanol industry residues has created new opportunities for new value-added products, especially in Brazil,
where they are produced in high quantities. 相似文献
978.
The reactions of 2,4-dinitrophenyl and 2,4,6-trinitrophenyl methyl carbonates (DNPC and TNPC, respectively) and S-(2,4-dinitrophenyl) and S-(2,4,6-trinitrophenyl) ethyl thiolcarbonates (DNPTC and TNPTC, respectively) with a series of benzenethiolate anions were subjected to a kinetic investigation in water, at 25.0 degrees C, and an ionic strength of 0.2 M (KCl). These reactions obey pseudo-first-order kinetics, under excess of benzenethiolate, and are first order in the latter reactant. However, comparable reactant concentrations were used in the reactions of 4-nitrobenzenethiolate anion with TNPC and TNPTC, which showed second-order kinetics. The nucleophilic rate constants are pH independent, except those for the reactions of TNPC with 4-methoxy- and pentafluorobenzenethiolates, and TNPTC with benzenethiolate and 4-chloro- and 3-chlorobenzenethiolates, which show acid dependence. The Br?nsted-type plots for the nucleophilic rate constants are linear with slopes beta = 0.9, 1.0, 0.9, and 0.9 for the reactions of DNPC, TNPC, DNPTC, and TNPTC, respectively. No break in the Br?nsted plot was found for the reactions of DNPC and DNPTC at pK(a) ca. 4.1 and 3.4, respectively, consistent with concerted mechanisms. TNPC is more reactive toward benzenethiolate anions than DNPC, and TNPTC more than DNPTC due to the better leaving groups involved. Comparison of the kinetic results obtained in this work with those for the concerted phenolysis of the same substrates shows that benzenethiolate anions are better nucleophiles toward carbonates than isobasic phenoxide anions. This is explained by Pearson's "hard and soft acids and bases" principle. 相似文献
979.
A methodology for the worst case measurement uncertainty estimation for analytical methods which include an instrumental quantification step, adequate for routine determinations, is presented. Although the methodology presented should be based on a careful evaluation of the analytical method, the resulting daily calculations are very simple. The methodology is based on the estimation of the maximum value for the different sources of uncertainty and requires the definition of limiting values for certain analytical parameters. The simplification of the instrumental quantification uncertainty estimation involves the use of the standard deviation obtained from control charts relating to the concentrations estimated from the calibration curves for control standards at the highest calibration level. Three levels of simplification are suggested, as alternatives to the detailed approach, which can be selected according to the proximity of the sample results to decision limits. These approaches were applied to the determination of pesticide residues in apples (CEN, EN 12393), for which the most simplified approach showed a relative expanded uncertainty of 37.2% for a confidence level of approximately 95%. 相似文献
980.
R. Parise Filho A. A. S. Araújo M. Santos Filho J. R. Matos M. A. B. Silveira C. A. Brandt 《Journal of Thermal Analysis and Calorimetry》2004,75(2):487-494
Oxamniquine (OXA) is a schistosomicide agent that causes some adverse effects in central nervous system. Intending to improve
OXA therapeutic properties, a polymeric prodrug was designed. Currently, there is an increasing interest of thermal analytical
techniques in the pharmaceutical area, so differential thermal analysis (DTA) and thermogravimetry (TG) were carried out to
evaluate the thermal behavior of OXA, polymethacrylic acid (PMA), [poly(methacrylic-co-oxamniquine methacrylate)acid] (PMOXA)
and physical mixture (OXA+PMA). The thermoanalytical profile of the physical mixture showed characteristic events of the thermal
decomposition of OXA and PMA. Distinctly, PMOXA DTA curve did not show an endothermic peak at 148.5°C indicating that the
drug was incorporated into the polymeric system. These results were corroborated by the IR spectroscopy and X-ray diffraction
data.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献